You probably think you know the answer to this question: just a couple of days, right? Wrong. In humans, yes, sperm cells stay viable for just about three days. If any babies are going to be made, it has to be within that short time window. But human sperm cells are actually the fragile minority. Many female animals, after having mated, store sperm cells for long time periods. Bats, for example, often mate in autumn and then hibernate with live sperm in their oviducts, which only become active in the next spring. And social insects such as ants are even more extreme: they mate just once in their life and then set up a nest, producing workers, sometimes for years or even decades on end, all the while using that single sperm larder from their bridal flight. Ant sex and many more myrmecological marvels are dished out in this delightful video interview of Field Museum in Chicago curator Corrie Moreau. With thanks to my Penguin editor Melanie who discovered it!